Vacuum system



Sept. 22, 1964 FcP-AGANO VACUUM SYSTEM Filedbec. 15, 1951 [nu enter-E's/7k agano by a M H115 Attorney United States Patent 3,149,775 VACUUMSYSTEM Frank Pagano, Schenectady, N.Y., assignor to General ElectricCompany, a corporation of New Yorlr Filed Dec. 13, 1%1, Ser. No. 159,0%'7 Claims. (ill. 230-69) The present invention relates to vacuum systemsof the type in which very low pressures and temperatures are to bemaintained and, in particular, to methods and apparatus for removinghydrogen from such systems.

With the impetus toward the successful launching of satellites andvehicles into space, there isa growing need for extensive testing ofsuch vehicles and components thereof under conditions substantiallyduplicating spatial environment. While it is essential that allinformation possible be obtained with respect to the operation of aspace vehicle in earth orbiting or space travel missions, it is alsodesirable that this information be obtained rapidly and under conditionswhich can be controlled more accurately and flexibly and at less expensethan sending such vehicles or satellites into space itself.

In the copending application of Donald J. Santeler,

.Serial No. 59,642, filed September 30, 1960, there is disclosedapparatus for producing low pressure conditions within a spacesimulating chamber in which mechanical and diffusion type pumps are usedfor rough evacuation of the chamber and a cryogenic pumping apparatus,consisting of either liquid nitrogen or liquid hydrogen refrigeratingapparatus or both, is used to produce the final low pressure. One of theproblems encountered in such space simulating apparatus is that ofremoving hydrogen from the evacuated space. This gas is not readilyremoved by pumping utilizing cryogenic techniques, since temperatureslower than 4 K. are required to condense hydrogen at the pressure ofless than l0' mm. of mercury desired in space simulating chambers. Theproblem of removing hydrogen is further intensified in such chamber whenthey are used for testing engines, such as rocket engines, which exhausthydrogen containing gases. Under such conditions, it is necessary toremove large amounts of hydrogen to maintain test conditions similar tothose which might be encountered in outer space.

In the copending application of Virgil L. Stout and James R. Young,Serial No. 158,460, filed December 11, 1961, there are disclosed methodsand apparatus for pumping hydrogen in which a hydrogen permeable member,such as a palladium or palladium alloy diaphragm, is exposed to anoxidizing atmosphere subjected to higher hydrogen pressure so that thediaphragm operates to pror vide a pumping function and to transfer thehydrogen from a region of low hydrogen pressure to a region having ahigher average hydrogen pressure.

The chief object of the present invention is to provide new and improvedmethods and apparatus for removing hydrogen from a vacuum systemoperating at very low hydrogen pressures.

Another object of the invention is to provide an arrangement forsimulating conditions of space outside the earths atmosphere by removingnot only readily pumped and readily condensable gases, but also hydrogenunder conditions such that the gas is transferred from a region of lowerpressure to one of higher pressure.

A still further object of the invention is to provide a uniquecombination of pumping apparatus to simulate conditions in space beyondthe earths atmosphere.

In accordance with an important aspect of my invention, the conditionsexisting in space beyond the earths atmosphere are simulated in achamber by removing gases therefrom using mechanical and cryogenicpumping means and either thereafter or simultaneously removing hydrogenfrom the chamber by utilizing a material of the type 3,149,??5 PatentedSept. 22, 1964 through which hydrogen can permeate in atomic form andexposing one surface of the material to the atmosphere in the chamberand exposing the opposite surface of the material to an oxygencontaining atmosphere so that hydrogen enters into solution with thematerial in the surface exposed to the chamber and after passing throughthe material reacts with oxygen at its opposite surface to form water.

In accordance with another aspect of the invention, the hydrogencontained in gases which are developed in such a chamber when an engine,such as a rocket engine, is tested is rapidly removed by positioningsuch a hydrogen removing member within the chamber which is exposed tosuch gases, the member being hollow, and passing an oxygen containingatmosphere through the member.

The attached drawing illustrates preferred embodiments of the invention,in which:

FIGURE 1 is a view in section of a space simulator chamber employing thepresent invention;

FIGURE 2 is a sectional view illustrating the arrangement of hydrogenremoving apparatus with respect to cryogenic pumping apparatus used inthe chamber of FIGURE 1; and

FIGURE 3 is a sectional View of a hydrogen pumping apparatus utilizingthe apparatus shown in FIGURE 1.

The space simulator 1 illustrated in FIGURE 1 comprises an outerinsulated housing, including an upper insulated hemispherical shell 2, alower hemispherical shell 3, and a central cylindrical shell 4, theseelements together defining an evacuated chamber in which a test member,such as the rocket engine 5, is to be tested. A shell 6 located withinthe evacuated chamber provides means to absorb radiant energy. Asuitable reflector 7 is also located in the upper portion of thechamber, and a spherical cryogenic member 8 is mounted in the lowerportion of the chamber. Shell 6 is supported within the chamber by meansof a plurality of gusset plates 9, and spherical member 3 is supportedby rods 10 extending between gusset plates 9 and member 8.

Evacuation of the chamber in accordance with my invention is achieved bya combination of mechanical, diffusion, cryogenic and hydrogen pumpingmeans. The mechanical pumps (not shown) are, preferably, locatedexternally of the simulator chamber 1 and are connected thereto by meansof conduits 11 which extend through the cylindrical portion 4 of thehousing and radiant energy absorbing shell 6. The diffusion pumps 12which may be conventional in character, are attached to an opposite endof elbows 11. Pipes or conduits 13, connected to diffusion pumps 12,preferably, are connected to the external mechanical pumps.

The radiant energy absorbing shell 6 comprises a frustoconical shapedportion 14 and a cylindrical portion 14'. These portions, preferably,are fabricated of plate material to form a structure whose lower endsurrounds the upper portion of cryogenic pumping member 8. Heat exchangecoils 15 are, preferably, fastened and thermally connected to the platescomprising shell 6. A gas, such as liquid nitrogen, may be expanded orevaporated in coils 15. Since it is desirable that a temperature lessthan K. be maintained within the space simulating chamber, thistemperature may be readily achieved by expanding liquid nitrogen incoils 15, the liquid nitrogen upon expansion providing a temperature ofapproximately 77 K.

The cryogenic pumping member 8 comprises a plurality of panels 16 whichare fabricated to form a substantially spherical enclosure having anopening 17 through which a component, such as the rocket engine 5, maybe introduced for test purposes. Panels 16 are provided with refrigerantcoils 18 through which refrigerant gas, which again may be liquidnitrogen, may be passed.

A portion of the structure of the cryogenic member 8 is illustrated inFIGURE 2. As there shown, the panels 16 have heat exchange coils 13soldered or otherwise thermally attached in a conventional manner sothat gas expanding within the coils 13 is in heat exchange relation withwall 16. A plurality of battle fins 19 extend from wall 16 and arethermally connected thereto. With this construction, both the wall 16and the baffie fins 19 are maintained substantially at the temperatureof the coils 18 through which the refrigerant is circulated.

I also provide means to condense molecules of gases having boilingpoints less than the evaporation temperature of nitrogen. For thispurpose, condensing fins 20 are positioned below fins 19 and havethermally joined thereto refrigerant or heat exchange coil 21.Condensing fins 29 may be maintained at a temperature of the order, forexample, of 20 K. by passing through heat exchange coils 21 liquidhelium and allowing the liquid helium to expand in the coils.

In the structure thus far described, any radiant energy heat load isreadily exposed to and absorbed by the higher temperature nitrogenrefrigerant circuit comprising coils 15 while pumping of nitrogen,oxygen, argon, and carbon monoxide may be performed by the cryogenicpumping action of refrigerant coils 21 and fins Zil. One of theremaining problems in order to completely simulate conditions of spaceoutside the earths atmosphere is to remove the hydrogen gas present inthe space chamber and which may be present both in atomic and molecularform. This gas is not readily removed by utilizing cryogenic pumpingtechniques since temperatures lower than 4 K, the boiling point ofliquid helium, are required to condense hydrogen to equilibriumpressures less than 10 mm. of mercury required to duplicate spatialconditions. In order to remove such hydrogen gas, I provide hydrogenpumping apparatus which comprises one or more tubes 22 located at pointson the periphery of the chamber 1 and connected across openings in lowerhemispherical shell 3. Each of the tubes 22 comprises a first portion 23in which may be located a water cooled baflle 24 and a second portion 25in which are located one or more hydrogen pumping means 26. Hydrogenpumping means 26 are illustrated in FIGURE 3 as a hollow coil ofmaterial through which hydrogen can permeate in atomic form. Such amaterial may comprise, for example, palladium, iron, platinum, or alloysof such materials. One particularly suitable material comprises apalladium alloy consisting of 75% palladium and 25% silver. In such amaterial, hydrogen enters into solution which the material on onesurface thereof and permeates through the material in atomic form tolater pass out of solution at the other surface of the material Where itreacts with a gas present in the atmosphere at such other surface. Whenthe atmosphere at the exit surface includes oxygen, the hydrogen reactsto form water or water vapor. For this purpose, the coil 26 is formedfrom a hollow tube and a supply of oxygen, or of an atmospherecontaining oxygen, is passed through the coil entering through a conduit2'7 from an oxygen supply through a valve 23 and being withdrawn througha conduit 29 and a vacuum pump 3%.

As illustrated, in order to expedite the removal of hydrogen from thechamber 11, a plurality of coils 26 may be connected in parallel in eachtube 22 and in series through two or more of such tubes. Also,preferably, the coils 26 of the hydrogen permeable material in each tube22 are joined by tubes or pipes 31 through electrically insulatingleak-proof joints 32. Also, each coil of material Z6 is electricallyheated by means of current passing through wires 33, 3 1 and suppliedfrom a suitable source of voltage indicated conventionally by the signsplus and minus. In this manner, the temperature of the individual coils26 is raised preferably to a temperature somewhere between C. and 500 C.to accelerate the hydrogen pumping action. Alternatively, thetemperature of the individual coils 26 may be raised by heating theoxygen, or other oxygen containing atmosphere supplied through conduits27, to a temperature such that in passing through the tubes 26 it raisesthe temperatures of such tubes to a desired point. When electricresistance heating is used to raise the temperature of the coils 26,obviously suitable electrical insulating means 35 is supplied at theentry and exit points of the coils 26 through the walls of tube Asillustrated in FIGURE 3, the end of tube 25 remote from chamber 1 isclosed by a vacuum seal comprising a closure member 36 Welded across theend of tube 25.

In the operation of my vacuum system, the chamber 1 is first evacuatedby means of a mechanical system, or some equivalent external pumpingsystem, to reduce the pressure in the chamber. Thereafter, both thediifusion pump 12. and the cryogenic pumps comprising coils 15, 1 andcoils 21 are made operative by circulating liquid nitrogen through thecoils 15, 18 and liquid helium through the coils 21. By these means,gases having boiling points greater than 77 K. are condensed through theoperation of the cryogenic pumping coils 15 and 18. Those gases, such asnitrogen, oxygen and argon, having boiling points less than 77 K. at theoperating pressures, but higher than 20 K. are condensed through theoperation of the cryogenic pumping means comprising coils 21. Theremaining hydrogen gas within the chamber is allowed to pass freelythrough panels 16 through aperatures 37 in such wall and come in contactwith the coils 26 of the hydrogen pumping apparatus. To minimize theeffect of the heated coils 26 on the panel 16, water cooled battles 2 intubes 23 hide the hot coils 26 from refrigerated panel 16 which, inturn, shields the coils from the interior of the chamber itself. On theother hand, any hydrogen gas contained in the chamber, upon passingthrough openings 37, even though it is at a lower hydrogen pressure thanthe average hydrogen pressure on the inside of the tube 26, enters intosolution with the material of tube 26 since it is in an atmospheredevoid of oxygen. The hydrogen gas permeates through tube 26 to theopposite surface thereof where it reacts with the relatively oxygen richatmosphere to form water or water vapor. In this fashion, coils 26comprising the hydrogen pumping apparatus operate to perform a pumpingaction and to transfer hydrogen from a region of low hydrogen pressureto a region of higher average hydrogen pressure.

in the use of my improved vacuum system for a space simulating chamber,it is frequently desired to test components, such as rocket engine 5,which produce exhaust comprising hydrogen containing gases. During suchtests, very large amounts of hydrogen are produced rapidly. In order toquickly remove such excess amounts of beyond the earths atmosphere asrapidly as possible, I provide additional hydrogen pumping apparatuswithin the chamber in the vicinity of such a test rocket engine 5. Thisapparatus comprises a plurality of coils 38 of a material through whichhydrogen permeates connected in parallel with each other and in serieswith conduits 39 and it connected, respectively, to a source of oxygenor oxygen containing atmosphere and a vacuum pump. The coils 3 may alsobe formed of palladium or a palladium alloy and may be heated either byheating the oxygen or oxygen containing gases that pass through conduits39, 4t; and coils 33, or they may be heated by electrical means (notshown) similar to the electrical heating means illustrated in FIGURE 3.Additionally, they may be heated by the exhaust gases themselves to atemperature sufficient to accelerate the hydrogen pumping operation ofthe coils 38.

An important advantage of my improved vacuum systern is that it providesa method and apparatus for rapidly and easily removing hydrogen from aregion of low hydrogen pressure to a region of higher average hydrogenpressure. In this way, it can perform a function which is not performedthrough known cryogenic pumping apparatus. It thus obviates a problemparticularly encountered in space simulator chambers where theaccumulation of hydrogen, particularly when rockets or similar enginesare tested, poses a heretofore unsolved problem. By my combined hydrogenpumping apparatus, conventional mechanical pumping systems, anddiffusion and cryogenic pumping apparatus, I provide an arrangementwhich can more effectively and rapidly simulate conditions beyond theearths atmosphere.

While in the foregoing I have shown the hydrogen pumping apparatus to bein the form of coils, obviously any other arrangement of surfaces may beemployed. Thus, for example, palladium diaphragms may be employed and anoxygen containing atmosphere may be passed on one side of such adiaphragm while the hydrogen to be pumped is presented to the oppositesurface of the diaphragm.

While I have described preferred embodiments of my invention, it will beunderstood that my invention is not limited thereto since it mayotherwise be embodied in the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates are:

1. In a space simulating chamber of the type in which the operation ofmaterials and components at low pressures and temperatures is to beexamined,

a pump connected to said chamber to remove gases therefrom,

cryogenic means located in said chamber for condensing gases therein,

a first means for removing hydrogen from said chamber positioned alongthe outer surface thereof and a second means for removing hydrogen fromsaid chamber positioned within said chamber and adapted to be exposed tohydrogen containing gases generated within said chamber during operationof a component therein, said first and second means comprising ahydrogen permeable material.

2. The combination of claim 1 in which the means for removing hydrogencomprise palladium.

3. The combination of claim 2 in which the palladium has a first surfaceexposed to the atmosphere within the chamber and an opposite surfaceover which an atmosphere containing oxygen may be passed.

4. In the combination of claim 2, means for heating said first means toaccelerate the pumping of hydrogen from said chamber and means thermallyshielding said first means from the interior of said chamber.

5. A space simulating chamber of the type in which the operation ofmaterials and components at low pressures and temperatures is to beexamined comprising means for reducing pressure in said chamber to a lowvalue,

cryogenic means located in said chamber for condensing gases therein,and

means for removing hydrogen from the chamber comprising a tube ofpalladium containing material positioned to be exposed to hydrogencontained in said chamber,

means for heating said tube,

means for passing an oxygen containing atmosphere through said tubewhereby hydrogen within said chamber enters into solution with said tubeand permeates therethrough to react with such oxygen on the innersurface of said tube, and

means thermally shielding said tube from the interior of said chamber.

6. In combination, means defining a chamber to be evacuated,

a pump connected to said chamber to remove gases therefrom,

cryogenic means located in said chamber for condensing gases therein,and

means located at the periphery of said chamber for removing hydrogenfrom said chamber,

said hydrogen removing means comprising a palladium containing materialhaving a surface exposed to the atmosphere of said chamber,

means for exposing the opposite surface of said material to a flowingoxygen containing atmosphere,

means for heating said material to accelerate the removal of hydrogenfrom the chamber, and

means thermally shielding said material from the interior of thechamber.

7. A space simulating chamber of the type in which the operation ofmaterials and components at low pressures and temperatures is to beexamined comprising means for reducing the pressure in said chamber to alow value, and

means for removing hydrogen from the chamber comprising a palladiummember having a first surface exposed to hydrogen and other gasescontained in said chamber,

a second surface exposed to a flowing atmosphere having a hydrogenpressure higher than the hydrogen pressure to be obtained in saidchamber,

said atmosphere containing oxygen,

means for heating the palladium member to facilitate the removal ofhydrogen from said chamber, and

means thermally sealing said member from the interior of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES 1958 Vacuum Symposium Transactions, published by PergamonPress, Incorporated (New York), 1959 (article by Barley et al., on pages262-267 relied on).

1. IN A SPACE SIMULATING CHAMBER OF THE TYPE IN WHICH THE OPERATION OFMATERIALS AND COMPONENTS AT LOW PRESSURES AND TEMPERATURES IS TO BEEXAMINED, A PUMP CONNECTED TO SAID CHAMBER TO REMOVE GASES THEREFROM,CRYOGENIC MEANS LOCATED IN SAID CHAMBER FOR CONDENSING GASES THEREIN, AFIRST MEANS FOR REMOVING HYDROGEN FROM SAID CHAMBER POSITIONED ALONG THEOUTER SURFACE THEREOF AND A SECOND MEANS FOR REMOVING HYDROGEN FROM SAIDCHAMBER POSITIONED WITHIN SAID CHAMBER AND ADAPTED TO BE EXPOSED TOHYDROGEN CONTAINING GASES GENERATED WITHIN SAID CHAMBER DURING OPERATIONOF A COMPONENT THEREIN, SAID FIRST AND SECOND MEANS COMPRISING AHYDROGEN PERMEABLE MATERIAL.